Mitosis and Cytokinesis Lab
By Dr. Leah Howell, Dalton State College
Introduction
All cells come from preexisting cells, and eukaryotic cells must undergo mitosis in order to form new cells. The replication of a cell is part of the overall cell cycle (Figure 1) which is composed of interphase and M phase (mitotic phase). M phase, which consists of mitosis and cytokinesis, is the portion of the cell cycle where the cell divides, reproducing itself. Mitosis is the division of the nucleus and its contents.
In mitosis, DNA which has been copied in S phase of interphase is separated into two individual copies.
Each copy will end up in its own cell at the end of M phase. Mitosis has several steps: prophase,
prometaphase, metaphase, anaphase, and telophase (Figure 2). The spindle fibers, which are formed by the cell as mitosis progresses, are used to attach to chromosomes, align them down the middle of the cell, and pull chromosomes apart into their identical individual chromatids which will end up in separate cells. As mitosis is nearing its end and the cell is in telophase, the cytoplasm also divides so that both new cells will have their own fluid, organelles, etc. This division of the cytoplasm is called cytokinesis.
Mitosis and cytokinesis can be viewed under a microscope.
Figure 1- The cell cycle. Biology. OpenStax College.
Exercise 1: Mitosis of onion root tip
(Adapted from Cell Biology Laboratory Manual Online Dr. William H. Heidcamp, Biology Department, Gustavus Adolphus College, St. Peter, MN 56082 -- cellab@gac.edu)
Materials
Prepared slide of onion (allium) root tip
Microscope
Procedure
1. Obtain a slide of allium root tip for observation of the stages of mitosis in a plant cell.
2. Examine the slide under a microscope.
3. Draw and label all stages of mitosis below. Figure 3 can be used for help with this.
Interphase Prophase Metaphase
Anaphase Telophase and Cytokinesis
Exercise 2: Mitosis of whitefish blastula
(Adapted from Cell Biology Laboratory Manual Online Dr. William H. Heidcamp, Biology Department, Gustavus Adolphus College, St. Peter, MN 56082 -- cellab@gac.edu)
Materials
Prepared slide of whitefish blastula
Microscope
Procedure
1. Obtain a slide of a whitefish blastula for observation of the stages of mitosis in an animal cell.
Since early embryogenesis involves rapid cellular division, the whitefish blastula has long served as a model of mitotic division in animals. It also has the advantage of demonstrating clear spindle formation in the cytoplasm.
2. Examine the slide under a microscope.
3. Draw and label all stages of mitosis below.
Interphase Prophase Metaphase
Anaphase Telophase and Cytokinesis
Exercise 3- Simulating mitosis using beads Materials
Baggy full of beads and strings
Procedure
1. Organize beads into “chromosomes” as shown in Figure 4.
2. Simulate the steps of interphase (specifically S phase) and then M phase using the beads. Hint:
The chromosomes in Figure 4 have not been through S phase yet, so you will eventually need
more beads than are shown in Figure 4. The strings in the bag are used to simulate spindle
fibers.
Exercise 4: Non-disjunction events during meiosis
Failure of chromosomes to separate during mitosis or meiosis will result in an incorrect number of chromosomes in daughter cells. This occurrence is known as non-disjunction, and it is often triggered by a lapse during a mitotic checkpoint. Should non-disjunction occur during meiosis, the resulting egg or sperm cell will have an incorrect number of chromosomes; if this sex cell is then fertilized, the fetus will have a chromosomal abnormality. The term given for having an incorrect number of chromosomes is aneuploidy. A common type of aneuploidy is trisomy, which is when there are 3 copies of a particular chromosome instead of 2. Several common chromosomal abnormalities are listed in the table below.
The most common trisomy that a human can survive is Down syndrome, which occurs at chromosome 21. To diagnose a chromosomal abnormality, doctors use a map of the chromosomes known as a karyotype. Each chromosome pair is laid out side-by-side so it is relatively easy to determine if there are any irregularities. Referring to the karyotype below, it is clear that each chromosome pair is present and of relatively equal length. Note that last chromosome pair (23) is labeled X/Y; these chromosomes are the only 2 that do not exactly match.
Chromosome pair affected
Type Diagnosis
13 trisomy Patau Syndrome
18 trisomy Edwards Syndrome
21 trisomy Down Syndrome
23 (XO) monosomy Turner Syndrome 23 (XXY) trisomy Klinefelter syndrome
"Human male karyotype" by Courtesy: National Human Genome Research Institute - From w:en:Image:Human male karyotpe.gif, Uploaded by User:Duncharris.. Licensed under Public Domain via Wikimedia Commons
